Device for reproducing sound



May 30, 1939. A; T. VAN URK 'Er AL l 2,160,112

DEVICE FOR REPRODUCING SOUND Filed Jan. 9, 1956 Patented May 30, '1939 PATENT oFFicE.

2,100,112 D Evlcnron nEPaoDUcrNG soUNn Arend Thomas Van Urk and Roelgfflgfmeulen, Eindhoven, Netherlands, assignors to N; V.

P h 1 li ps Gloeilampenfabrieken, Eindhoven,

Netherlands Application January 9, 193s, serial No. 58,430

In Germany January 17, 1935 'i Claims.

Our invention relates-to a device for reproducing soundy by means of a plurality of sound radiators.

To reproduce sound as uniformly as possible throughout the entire-frequency band to be reproduced, it has been proposed to divide the frequency band'into several regions or zones and to provide for each of these regions one or more sound radiators, which are supplied with substantially only the frequencies lying within the corresponding region, Such a method of reproduction was based on the assumption that the outstanding resonances of the corresponding sound radiators had to be utilized, as these resonances could be readily selected as to frequency,

and owing to their juxtaposition, a substantially rectilinear frequency curve and an especially high eiiiciency could be obtained. With such a method the qualityof the reproduction was much better than that obtained when using a single sound radiator for the entire frequency band.

In such methods of reproduction, the sound radiator or radiators used for reproducing the low tones, i. e., low frequencies, were provided with comparatively large conical diaphragms having, for example, a radiating-surface diameter of the order of 10 inches or more. The radiators used for reproducing the high tones, i. e., high frequencies, were provided with smaller conical diaphragms having.l for instance, a radiatingsurface diameter of approximately 6 inches or less.

Such a selection of diaphragm sizes appeared to be'logical because the lower tones, as a rule,

- have a larger amplitude of movement than do the higher tones. If--for reproducing the low tones-a single sound radiator having a diaphragm smaller than that indicated above were to be used, the diaphragm would have to vibrate 40 through considerably larger amplitudes, which would entail manufacturing diiliculties.` Such difficulties were avoided by using for reproducing the low tones, sound radiatorswhose diaphragms Y had a radiating-surface diameter of at least 10 inches.

After extensive experimental and development work in connection with loudspeakers for different types of reproduction, for instance, radio, talking pictures, etc., it has been found that the reproduction obtained by any of the present reproducing methods did' not meet present demands, and that it is very desirable to improve the quality of reproduction even at the expense of reducing the eiciency. Furthermore, it is necessary to reproduce a considerably wider frequency band, i. e., a band having a characteristic frequency curve which is substantially rectilinear up to frequencies of at least 8,000 cycles.

Our invention has for its object to improve the quality of sound reproduction beyond that ob- 5 tainable at present, and is basedV on a fundamentally diierent principle from that used up to the present time in reproducing sound by division into frequency regions and using corresponding sound radiators. l0

We have found that thereproduction over the entire frequency band can be greatly improved by utilizing the following two facts: (a) that the frequency value of the mutually-corresponding resonances of geometrically-similar conical or the Alli like diaphraghs are approximately inversely proportional to .the size of the radiating surfaces of the Ydiaphra'gins; and (b), that a diaphragm has many resonances which are less strongly damped in the low-frequency region, but are strongly 20 damped, i. e., considerably smoothed, in the highfrequency region.

In accordance with our invention, which is based on the above facts, we use for reproducing the lower frequencies, i. e., frequencies within a 25 region having an upper limit between about 200 and 500 cycles, electrodynamic sound radiators having conical or the like diaphragms and having a ilrst (or fundamental) resonance lying below about 50 cycles, and a secondA (or first dia- 30 phragm) resonance-which usually has the most `disturbing effect-lying above the highest frequency to be reproduced in this region. For reproducing the higher frequencies we preferably provide one or more sound radiators whose out- 35 standing resonances, i. e., fundamental resonance, and also for example, rst diaphragm resonance,

11e below the upper limit of the low-frequency region.

As distinguished from fdiaphragm resonance, 40 the term fundamental resonance, as used herein and in the claims, is to be understood to mean the resonance determined by the mass of the diaphragm and its suspension.

Thus, in accordance with the invention, the 45 frequencies lying Within the low-frequency region are reproduced without the aid of resonance, whereas the frequencies above the low frequency region are reproduced by the almost exclusive use of smoothed diaphragm resonances. With 50 such amethod of reproduction it is possible to obtain a quality which is considerably higher than that obtained by prior art devices or methods.

Although it has been proposed to reproduce 55 sound by means of a single loudspeaker having a conical diaphragm and having no natural resonance inthe most important portion of the entire frequency band to be reproduced, in such' cases it was considered important to reproduce only the frequencies up to about 2000 cycles. Apart from the fact that it is impossible to use in practice a loudspeaker having its second resonance at about 2000 cycles, such a method does not meet the requirements of quality reproduction overan extended frequency range and of eiliciency. To meet the requirements of the present invention with this prior art method, it would be necessary to use a loudspeaker having a flrst diaphragm resonance lying at about 8000 cycles. Such a loudspeaker could not be constructed so as to obtain the required rigidity of the diaphragm, because the diaphragm would have to be made so heavy and small that the efficiency would be reduced to a value which would make the speaker unsuited for practical purposes.

In order that our invention may be clearly understood and more readily carried into effect, we shall describe same more fully with reference to the accompanying drawing,v in which:

Figure l is a schematic rear view in perspective of a sound-reproducing device in accordance with the invention;

Fig. 2 is a graph for use .in explaining the operation of the device shown in Figure 1.

The sound-reproducing device shown in Figure l comprises a suitably-supported bafe 9 upon which are mounted, so as to freely radiate the sound forward, two groups C and D of sound radiators, for instance loudspeakers. Group C, which serves to reproduce the lower frequencies, is shown as consisting of eight loudspeakersm, whereas group D, which serves to reproduce the higher frequencies, is shown as consisting of a single loudspeaker I0. Loudspeakers 8 and IU, and particularly loudspeakers 8, are of the electrodynamic type, as in this case the resonances can be fixed in a simple manner at the required frequency values.

Loudspeakers 8 have their voice-coils connected in parallel by conductors I and I6, which conductors are connected by conductors i9 and 20 respectively to the output side of a device II, whereas loudspeaker I0 is connected through conductors I1 and I8 to the output side of a second device I2.

The devices II and I2 have their connected in parallel by conductors 2| and 22, which conductors are connected by conductors I3 to a suitable source (not shown) for supplying the entire frequency range to be reproduced by the speakers of groups C and D. The device II Iinput sides consists of the usual amplifying equipmentvemles.,

ploying amplifying tubes and a band by-pass filter whereby only frequencies of low value, for instance from about 20 to 300 cycles, are supplied to the speakers 8. Similarly, the device I2 consists of suitable amplifying and filtering equipment whereby only high frequencies. for instance frequencies above 300 cycles, are supplied through conductors I1 and I8 to speaker Ill. As the construction of such amplifying and filtering devices is Well known in the art, it is believed that their detailed illustration and description is unnecessary.

The loudspeakers 8 are provided with conical diaphragms having a diameter of not more than 8 inche's, and preferably between 5"/8 inches and 6% inches. vWith a conical diaphragm of such size it is easy to insure that its first resonance lies at such a high frequency as to cause no deleterious effect upon reproduction in the low-frequency region; a first diaphragm resonance between about 200 and 500 cycles being readily obtained without difficulty. No `use is made of the remainling diaphragm resonances, as these are located out-side the corresponding low-frequency region. Furthermore, by selecting "a very resilient suspension for the diaphragm, andnwitheihe. aid

of technical means known per se, it is possible to insure that the fundamental resonance lies below cycles; i. e., considerably lower than the lowest frequency to be reproduced in the low-fiequency region.

To obtainV affsufiicientlyhiglrsound intensity,

production a plurality of sound radiators, each having its own actuating system; all the radiators being actuated in the same phase. In Figure 1. group C is shown as consisting of eight loudspeakers; however, the number used depends upon conditions.. Thus it is seen that in distinction to known devices in which a single loudspeaker is used for reproducing the low tones, the device according to the invention has the characteristic feature that the -requiredradiating surface area is distributed over a large number of smaller surfaces with the result that not only the quality of reproduction but also the sound intensity is increased.

The loudspeakers for reproducing the higher frequencies, for instance the loudspeaker I0,

should preferably have a conical diaphragm-of a diameter of at least 8 inches and preferably 91/2 inches. Such diaphragms may be readily suspended and manufactured so that thefunda'- Y Y Y' mental resonance and the 'rst diaphragm Vresonance are located below about 200 to 500 cycles', and thus fall outside of the high-frequency region. Thus the various other partial resonances, which are present in large number, may be located above the range 200 to 500 cycles so that they substantially determine the frequency characteristic curve in the high-frequency region. These partial resonances increase the efficiency of the reproduction in this region, and are smoothed to such a degree that they have no physiological disturbing effect upon the reproduction.

As in some instances the physiological audible interval between the first and second diaphragm resonances may be so great as to produce an undesired dale in the frequency curve, it is preferable that not only the fundamental resonance, and the first diaphragm resonance but also the second diaphragmresonance lie below the lower limit of the high-frequency region. With this in view, it is advisable in most cases to locate the beginning of the second or high-frequency region at a frequency corresponding to the second diaphragm resonance, or even to one of the following resonances. For this purpose the loudspeaker I0 should be provided with a preferable conical diaphragm having a radiating surface diameter of about 9% inches, as by increasing the size of the radiating surface the diaphragm resonances are shifted towards the lower frequencies and out of the high-frequency range.

If the less disturbing efl Hg 15, it is preferable to use for the low-frequency Vre-` Y.

2,100,112 teristic of the invention is, however, in reproducv ing the low frequencies with a plurality of suitably-selected small conical diaphragxns; the number of which is generally greater than the number of speakers used for -the high-frequency reproduction. A

Although a single loudspeaker Il constructed on the above-mentioned lines and having a diameter of about 93/4l inches may be used for reproducing the frequencies above from 200 to 500 cycles, it is preferablein those cases in which it is desired to reproduce particularly high.v frequencies, for instance frequencies up to 10,000 cycles or more, to subdivide this second or highfrequency region into a third region, and to provide a separate speaker .for this'region. As the energy required for actuating suchl aspeaker is small in comparison withthe energy required for the other frequency region, a much smaller loudspeaker may be used A.for this purpose. In this manner a better reproduction is obtained without the entire installation'being madeappreciably more expensive. l

Very satisfactory results have been obtained with a device wherein the separation between.the low and high frequency 'regions take's place at about 200 cycles, and in which there is about six to ten times as many loudspeakers for the low-A frequency region as for the high-frequency region. 1

It may be necessary in some cases, for example to obtain the desired sound intensity in a large room, to use a second or third loudspeaker for the higherl frequencies while retaining the same size diaphragm; however, in such cases the ratio between the number of loudspeakers for the low frequency reproduction and= for lthe high frequency reproduction should be maintained substantially'the same.

It may also be necessary to provide a plurality of loudspeakers for the high-frequencyreproduction in order to overcome a disturbing directional effect; however, a single radiator of the Asame diaphragm size would be suilicient as far as the sound intensity is concerned. In such cases the energy supplied to each loudspeaker may of course be decreased, depending upon the number of speakers used.

From the above it is seen that the proportions between the sizes and the number of diaphragms of the present invention is just the opposite to those of prior art devices for reproducing sound by means of a plurality of sound radiators pertaining to different regions.

'Ihe operation of a device according to the invention will be more clearly understood by refervring to Figure 2, in which the abscissae represent quency reproducers.

Curve I is a reproduction curve of the sound radiatoror group of'h sound radiators, for in stance, the loudspeakers 8, to which are supplied the low frequencies falling within the-zone A. From this curve it is seen that the sound radiators employed for reproducing the lower frequencies have two outstanding resonances, n amely, a rst fundamental resonance, i. e., resonancel of the cone and suspension, lying at about 8 stantially rectilinear and horizontal cycles, as indicated at l; and a second resonance, i. e., first cone resonance, lying at about 500 cycles, as indicated at 2. As both these resonances lie outside the zone A they have no influence upon the reproduction of the frequencies within this zone.

Curve II represents a reproduction curve of the sound radiator or group of sound radiators; for instance the loudspeaker I to which are supplied the frequencies lying within the zone B, i. e., frequencies above 300 cycles. From curve II it is seen that the first resonances 5, 6, and 'I are more pronounced than are the other resonances, and also that the resonances 5 and 6 lie entirely outside-of zone B, and hence have noinfluence upon the reproduction of the frequencies lying within this zone. Although the resonance. 1 lies. partly within the zone B, it-

has no deleterious effect upon the reproduction because the resonance peak is somewhat fiat.

'I'he remaining portion of curve II forms a concatenation of strongly smoothed resonance peaks, and for practical purposes this portion of the curve may 'be considered as being substantially rectilinear upto about 10,000 cycles, at which point it drops rapidly.

Thedot-dash curve III'represents the total o resulting reproduction throughout the zones A andB, and itis seen that this curve has a subcourse throughout both zones.

Although in Figure l we have shown a reproducing device of a particular construction, suitable, for instance, for use behind the screen in talking picturework, our invention is not limited to any particular relative arrangement of the separate speakers. For example, in view of the known directional effect of the loudspeakers used for reproducing the high frequencies, it is frequently advisable to arrange a plurality of such loudspeakers so as to radiate the sound in different directions in order to distribute these frequencies as favorably as possible throughout the reproduction room.

While we have described our invention in con- What we claim is: v

1. A device for reproducing sound comprising means for dividing the frequencies to be repro-r duced into a low-frequency region having an upper limit between 200 to 500 cycles and a highfrequency region, a plurality of electro-dynamic loudspeakers for reproducing the frequenciesV lying Within the low-frequency region and having free radiating daphragms, said loudspeakers having their fundamental resonances below and their second resonancesA above said low-frequency region, and an electro-dynamic loudspeaker for reproducing the frequencies lying within the highfrequency region, said latter loudspeaker having its outstanding resonances below and other of its resonances Within said high frequency region.

2. A device for reproducing sound comprising means for dividing the frequencies to be reproduced into a low-frequency region having an upper limit between 200 to llcycles and a highfrequency region, a plurality of electro-dynamic loudspeakers for reproducing the frequencies lying within the low-frequency region and having free radiating diaphragms, said loudspeakers having their fundamental resonances below and their -second resonances above said low-frequency region, and an electro-dynamic loudspeaker for reproducing the frequencies lying within the high frequency region, said latter loudspeaker having its resonances other than the outstanding resonances within said high-frequency region.

3. A device for reproducing sound comprising means for dividing the frequencies to be reproduced into a low-frequency region having its upper limit at about 300A cycles and a high-frequency region, a. plurality. of electro-dynamic loudspeakers for reproducing the frequencies lying within the low-frequency region and each having a free radiating diaphragm of a` diameter less than 8 inches, and an electro-dynamic loudspeaker for reproducing the frequencies lying within the high-frequency region, said latter speaker having its fundamental and second resonance below the high-frequency region and other of its resonances within the high-frequency region, said second loudspeaker having a diaphragm of a diameter greater than 8 inches.

4, AA device for reproducing sound comprising means for dividing the frequencies to be reproduced into a low-frequency region having its upper limit at about 300 cycles and a high-frequency region, a plurality of electro-dynamic loudspeakers for reproducing the frequencies lying within the low-frequency region and each having a free radiating diaphragm of a diameter less than 8 inches, said loudspeakers having their fundamental resonances below about 20 cycles and their second resonances above 300 cycles, and an electro-dynamic loudspeaker for reproducing the frequencies lying within the highfrequency region and having a diaphragm of a diameter of at least 10 inches, said latter speaker having its fundamental and second resonance below 300 cycles and other of its resonances within the high-frequency region.

5. A device for reproducing sound comprising means for dividing the frequencies to be reproduced into a low-frequency region having its upper limit at about 200 cycles and a high-frequency region, a plurality of electro-dynamic oudspeakers for reproducing the frequencies lying Within the low-frequency region and each. having a free radiating diaphragm, said loud-speakers having their fundamental resonances below 20 cycles and their second resonances above 200 cycles, and an electro-dynamic loudspeaker for reproducing the frequencies ,lying within the high-frequency region, said latter loudspeaker having its fundamental and second resonance below 200 cycles and other of its resonances within the high-frequency region, the number of the low-frequency loudspeakers being from 6 to 8 times greater than the number of the high-frequency loudspeakers.

6. A device for reproducing sound comprising means for dividing the frequencies to be reproduced into a low-frequency region having an upper limit below 400 cycles and a high-frequency region, a plurality of electro-dynamic loudspeakers for reproducing the frequencies lying within the low-frequency region and having free radiating diaphragms, said loudspeakers having their fundamental resonances below and their second resonances above said low-frequency region, and an electro-dynamic loudspeaker for reproducing the frequencies lying within the high-frequency region, said latter loudspeaker having its outstanding resonances below and ,other of its resonances within said high frequency region.

7. A device for reproducing sound comprising means for dividing the frequencies to be reproduced into a lowfrequency region having an upper limit below 500 cycles and a high-frequency region, a plurality of electro-dynamic loudspeakers for reproducing the frequencies lying within the low-frequency region and having free radiating diaphragms, said loudspeakers having their fundamental resonances below and their second resonances above said low-frequency region; and an electro-dynamic loudspeaker for reproducing the frequencies lying within the highfrequency region, said latter loudspeaker having its outstanding resonances below and other of its resonances Within said high frequency region.

AREND THOMAS VAN URK. ROELOF VERMEULEN. 

